1. Field of the Invention
The present invention relates to an image forming apparatus that employs an electrophotographic system.
2. Description of the Related Art
In an image forming apparatus such as a color copier and a color laser printer, particularly in a tandem-type image forming apparatus, toner images of four colors, i.e., yellow, cyan, magenta, and black are sequentially transferred in a superimposing manner onto a recoding medium such as a belt or a sheet. The toner images of different colors may be relatively displaced due to various reasons. If the toner images of different colors are relatively displaced, toner images of the different colors can not be superimposing in a desired manner resulting in a color shift. Such color shift leads to reduced image quality so that it is necessary to take measures to avoid the color shift.
In a conventional technology such as that disclosed in Japanese Patent Application Laid-open No. H11-65208, the color shift is corrected in the following manner. That is, the toner images of yellow, cyan, magenta, and black for correction are formed onto a conveying belt that conveys a recoding sheet, and a detector optically detects the toner images. Furthermore, an amount of displacement between the color toner images is determined based on a result of the detection by the detector, and an exposing start time by an exposing unit is adjusted.
However, in the above conventional technology, toner is consumed for forming the toner images for correction, so that lesser images can be formed with the same amount of toner or extra toner is required for forming the same number of images.